It is assumed that a breakdown in the discrimination among memories is a major cause of forgetting. Studies in four areas were designed to determine the characteristics of materials and their contexts which are critically involved in establishing discriminations, in determining how these discriminations are weakened or lost, and the specific consequences of the loss. In the first area, the experiments were designed to exploit a recent finding that the simultaneous learning of several tasks reduces the forgetting rate for the tasks. The research in the second area seeks to determine if the interference produced by formal paradigms of interference can be reduced by simultaneous learning. The studies in the third area ask about the specific effects of interference within a list, and the experiments in the fourth area were intended to study the role of frequency memories using a short-term recognition paradigm.